1. Field of the Invention
The present invention relates to a method of fabricating a silicon nitride layer. More particularly, the present invention relates to a method of fabricating a silicon nitride layer with a high tensile stress.
2. Description of the Related Art
As semiconductor production shifted into the sub-micron regime, methods that can increase the driving current of NMOS and PMOS have become increasingly important especially for processes involving a feature size below 65 nm. Any increase in the driving current of NMOS and PMOS can significantly improve the time delay in the operating device.
In recent years, many experts on semiconductor fabrication start to investigate the effects of a silicon nitride cap layer or silicon nitride etching stop layer with preloaded stress on the driving current of a device. Through such research, it has been found that a silicon nitride layer with tensile stress can increase the driving current of an NMOS transistor. Furthermore, the larger the tensile stress in the silicon nitride layer, the higher will be the increase in the driving current of the NMOS transistor.
The best film-plating technique currently available for forming a silicon nitride layer can provide a tensile stress of at most 1.2 GPa. However, the preferred tension in the silicon nitride layer often exceeds the value of 1.2 GPa. Therefore, in the conventional technique, a rapid thermal annealing (RTA) process or an ultra-violet (UV) curing treatment is frequently performed after forming the silicon nitride layer to increase the tensile stress.
Furthermore, the silicon nitride etching stop layer for forming a contact opening is formed after forming a metal silicide compound. Thus, if a rapid thermal annealing process is applied to increase the stress in the silicon nitride etching stop layer, the high temperature created by the rapid thermal annealing operation will adversely affect the properties of the metal silicide material.
In addition, the UV curing treatment on a silicon nitride layer is carried out at normal atmospheric pressure so that the increase in tensile stress in the silicon nitride layer is quite limited. Hence, the UV curing treatment can hardly meet the demands for higher tensile stress in most semiconductor fabrication processes.
Thus, it is a major goal for most semiconductor manufacturers to find a method capable of increasing the tensile stress of a silicon nitride layer to such an extent that the demands in most processes are met and the driving current of the semiconductor devices is increased.